package java19_11_18;

import java.util.Scanner;

//青蛙跳台阶
public class Num6 {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        System.out.println(fun(n));
    }

    public static int fun(int n) {
        //终止条件
        if (n == 1) return 1;
        if (n == 2) return 2;
        //递归调用
        return fun(n - 1) + fun(n - 2);
    }
}
